We measured whether carbon loss in the form of sediment-associated microbial respiration differed between unvegetated sediments of recently constructed oil sands process-affected (OSPM) and reference wetlands. Constituents of OSPM-wetlands (increased salinity, conductivity) were expected to influence respiration, increasing gas (methane and carbon dioxide) flux and sediment oxygen demands (SOD) compared to reference wetlands. However, OSPM-wetlands released 1/10th the methane of reference wetland sediments but did not differ in CO2 ebulition. Sediment oxygen demand (SOD) rates were twofold higher in OSPM than reference wetlands; chemical SOD exceeded biological SOD for both wetland classes (~90% of total SOD). OSPM-wetland sediments, likely have less microbial activity and more chemical oxidation than reference wetlands. Carbon accrual is necessary for reclaiming Alberta boreal wetlands. Low microbial activity may promote carbon sequestration within OSPM-wetlands but high chemical SOD may limit available oxygen for benthos respiration.